2026 ICD-10-CM Diagnosis Code Q23.4Hypoplastic left heart syndrome

ICD-10-CM Codes›Q00-Q99›Q20-Q28›Q23

ICD-10-CM Q23.4
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

Q23.4 is a billable ICD-10-CM diagnosis code for hypoplastic left heart syndrome. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 306 through 307. The code is exempt from POA reporting. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Cardiac and circulatory congenital anomalies.

Code Identity

ICD-10-CM Code
Q23.4
Billable Status
Yes — Valid for Submission
Code Describes
Hypoplastic left heart syndrome
Short Description
Hypoplastic left heart syndrome
Same as the full description in the CMS dataset.
Parent Code
Q23
Congenital malformations of aortic and mitral valves

Code Classification

ChapterQ00-Q99Congenital malformations, deformations and chromosomal abnormalities
SectionQ20-Q28Congenital malformations of the circulatory system
CategoryQ23Congenital malformations of aortic and mitral valves
This CodeQ23.4Hypoplastic left heart syndrome

Present on Admission (POA)Billing

Q23.4 is exempt from POA reporting on inpatient claims to general acute care hospitals. Review other POA exempt codes.

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Hypoplastic left heart syndrome

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

External Cause of Injuries IndexGuidance

References for this code in the External Cause of Injuries Index.

    • Atresia, atretic
      • aortic (orifice) (valve)
        • congenital with hypoplasia of ascending aorta and defective development of left ventricle (with mitral stenosis)
    • Atresia, atretic
      • aortic (orifice) (valve)
        • in hypoplastic left heart syndrome
    • Atresia, atretic
      • mitral valve
        • in hypoplastic left heart syndrome
    • Development
      • defective, congenital
        • left ventricle
          • in hypoplastic left heart syndrome
    • Hypoplasia, hypoplastic
      • aorta, aortic
        • ascending, in hypoplastic left heart syndrome
    • Hypoplasia, hypoplastic
      • aorta, aortic
        • valve
          • in hypoplastic left heart syndrome
    • Hypoplasia, hypoplastic
      • left heart syndrome
    • Syndrome
      • hypoplastic left-heart

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR MAL001
Cardiac and circulatory congenital anomalies
Default principal diagnosis: inpatient Yes · outpatient Yes

Clinical InformationClinical

  • Hypoplastic Left Heart Syndrome

    a condition caused by underdevelopment of the whole left half of the heart. it is characterized by hypoplasia of the left cardiac chambers (heart atrium; heart ventricle), the aorta, the aortic valve, and the mitral valve. severe symptoms appear in early infancy when ductus arteriosus closes.

Patient EducationClinical

Congenital Heart Defects

Congenital heart defects (CHDs) are problems with the structure of the heart. "Congenital" means that that the problems are present at birth. These defects happen when a fetus's heart doesn't develop normally during pregnancy. Congenital heart defects are the most common type of birth defect.

The full article covers:

  • What are congenital heart defects?
  • What causes congenital heart defects?
  • Who is more likely to have a baby with a congenital heart defect?
  • What are the symptoms of congenital heart defects?
  • What other problems do congenital heart defects cause?
  • How are congenital heart defects diagnosed?
  • What are the treatments for congenital heart defects?

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Convert Q23.4 to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
746.7 Hypoplas left heart synd
Exact Match The mapping is direct, with no qualifiers.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About Q23.4Overview

Is Q23.4 (Congenital malformations of aortic and mitral valves) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report hypoplastic left heart syndrome on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does Q23.4 group to?

When hypoplastic left heart syndrome is the principal diagnosis on an inpatient stay, it groups to MS-DRG 306, 307, with relative weights from 0.9132 to 1.5758 depending on complications. Higher weights mean higher Medicare reimbursement.

Is Q23.4 exempt from POA reporting?

Yes. CMS lists this code among those exempt from present on admission reporting, so hospitals do not assign a POA indicator for hypoplastic left heart syndrome on inpatient claims.

What is the ICD-9 equivalent of Q23.4?

Under the General Equivalence Mappings, hypoplastic left heart syndrome converts to ICD-9-CM 746.7 (hypoplas left heart synd). The mapping is a direct match.

Footnotes

[1] Chronic - a chronic condition code indicates a condition lasting 12 months or longer and its effect on the patient based on one or both of the following criteria:

  • The condition results in the need for ongoing intervention with medical products,treatment, services, and special equipment
  • The condition places limitations on self-care, independent living, and social interactions.